The first meeting in four years between the GOP’s highest-ranking elected official and its presumptive nominee didn’t resolve significant differences — or yield an endorsement.

Paul Ryan, the speaker of the House and the highest-ranking elected Republican official, remains on a collision course with Donald Trump on both tone and policy, from the latter’s nativist rhetoric that has alienated minority voters to the constitutional conception of the presidency itself. That spells trouble for the GOP, which is desperately seeking unity ahead of this summer’s convention, especially because polls show Democratic front-runner Hillary Clinton would likely beat Trump in the general election.

“Look, it’s no secret that Donald Trump and I have had our differences,” Ryan said Thursday in a press conference at the U.S. Capitol after a morning meeting with Trump, his first real sit-down with the real-estate magnate. The 45-minute meeting didn’t seem to resolve those differences — and did not produce an endorsement from Ryan, an unprecedented state of affairs for the Republican Party at this stage of the campaign.

After the meeting, Ryan described Trump as “a very warm and genuine person.” But asked about the two men’s very different definitions of conservatism — they differ on free trade, immigration, and banning Muslims from entering the country, among other issues — Ryan praised Trump for attracting new voters but implicitly criticized his divisive language.

“He’s bringing new voters that we’ve never had for decades. That’s a positive thing,” Ryan said. But he asked later, “How do we keep adding and adding voters while not subtracting any voters?”

Ryan, like other Republican leaders such as Republican National Committee Chairman Reince Priebus, who was at the meeting, is charged with restoring a semblance of unity to a party that sorely lacks it. He has shown frustration with repeated calls for him to jump into the presidential race, viewing that as a distraction from his attempt to craft a forward-looking agenda for the party that can serve as a foil to President Barack Obama’s legacy and Clinton’s policy proposals.

With the meeting, the House speaker sought to find common ground with Trump and stressed what he called the “core principles that tie us all together: principles like the Constitution, the separation of powers, the fact that we have an executive that has gone way beyond the boundaries of the Constitution.”

Ryan, who was Mitt Romney’s running mate in the 2012 presidential election, has long railed against the Obama administration for what he views as abuses of executive power, from health care and immigration reform to efforts to close the U.S. military prison at Guantánamo Bay, Cuba, and the U.S.-led fight against the Islamic State.

In dealing with Trump, though, Ryan might find that the power of the presidency doesn’t offer much common ground after all. In Trump’s bombastic campaign trail pledges, he has promised almost unprecedented aggression in wielding the powers of the presidency against adversaries and allies alike, from scrapping decades-old alliances to toying with default on the national debt. And he’s doubled down on policies — such as barring Muslims from the United States — that observers have criticized as likelyunconstitutional, illegal, or unworkable.

Crafting a winning GOP platform despite these differences ultimately may elude the two men. Last week, after Ryan had declined to endorse him, Trump said, “I am not ready to support Speaker Ryan’s agenda. Perhaps in the future we can work together and come to an agreement about what is best for the American people.”

Trump has alienated a broad swath of minority voters, including Hispanics, African-Americans, and women, helping him notch record-high unfavorability ratings. That divisive language appears to be driving minority groups to mobilize against him, which is a huge concern for Ryan and his Senate colleagues who worry that having Trump at the top of the ticket could lead to a bloodbath in House and Senate races this year.

Trump met with some of those senators on Thursday. While many have begun to fall in line behind their nominee, they still struggle to give a full-throated endorsement of his more controversial policies, especially on national security. Trump’s “America First” isolationist take on foreign affairs, in particular, has rattled party leaders.

Ryan’s spokeswoman AshLee Strong said his office and Trump’s team will hold more in-depth policy conversations. But she also said that Ryan’s blueprint for GOP policy — dubbed “Confident America” — will be unveiled this summer, independently. That could put the two men on a collision course over potentially dueling party platforms, just in time for the convention in Cleveland that Trump hopes will be his coronation.

“We just began the process,” Ryan said. “And going forward, we are going to go a little deeper into the policy weeds to make sure that we have a better understanding of one another.”

Photo credit: Anadolu Agency / Contributor

Molly O’Toole is a senior reporter at Foreign Policy, covering immigration, refugees, and national security. She was FP’s sole 2016 presidential campaign reporter, on the trail from New Hampshire to Nevada. Previously, she covered the politics of national security for Atlantic Media’s Defense One, where she reported from Congress, the White House, the Pentagon, and the State Department. Before that, she was a news editor at the Huffington Post. Molly has also reported on national and international politics for Reuters, the Nation, The Associated Press, and Newsweek International, among others, from Washington, New York, Mexico City, and London. She received her dual master’s degree in journalism and international relations from New York University and her bachelor’s from Cornell University and in 2016 was a grant recipient of the International Women’s Media Foundation. She will always be a Californian. @mollymotoole